Organic light-emitting diodes (OLEDs) have attracted much attention over past three decades, owing to their high potential in next generation displays and lighting panels. However, before mass production of OLEDs for the consumer market can start, a long operating lifetime must be ensured. An elegant way to meet this requirement is to stack a number of OLEDs on top of each other, which is the so called tandem OLEDs technology. In a tandem OLED, the interconnecting units between two sub-OLEDs that serve as charge generation layers (CGLs) are required when driving OLED stacks as two-terminal devices. Up to now, several CGL structures have been reported, such as n-doped electron transporting layer (ETL)/p-doped hole transporting layer (HTL) (e.g., Alq3(Tris(8-hydroxyquinolinato)aluminium): Li(Lithium)/NPB(ninhydrin petroleum ether):FeCl3 (iron chloride)), organic p/n junction (e.g., CuPc(Copper(II) phthalocyanine)/F16CuPc(Copper(II) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine), Pentacene/C60 (Buckminsterfullerene)) and n-doped ETL/electron acceptor/HTL structure (e.g., BCP(Bathocuproine):Li/MoO3 (Molybdenum trioxide)/NPB, Bphen(Bathophenanthroline):Li/HAT-CN(1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile)/NPB). Among them, the use of transition metal oxides (TMOs), such as WO3 (Tungsten trioxide), MoO3, V2O5(Vanadium oxide) and ReO3 (Rhenium (VI) oxide) as the electron acceptor in the n-doped ETL/electron acceptor/HTL structure has been intensively studied, due to their low cost, easy synthesis and easy handling compared to their organic counterpart. To achieve the long term stability of tandem OLEDs, the CGL itself should be stable enough under the electrical stressing. However, the current type of n-doped ETL/TMO/HTL CGL is typically not stable enough for practical use. Therefore, approaches that can further improve the stability issue are desirable.